Aligned nanotube bearing composite material

ABSTRACT

A composite material including an arrangement of approximately aligned nanofilaments overlying at least another arrangement of approximately aligned nanofilaments, the longitudinal axis of the nanotubes of the first arrangement being approximately perpendicular to the longitudinal axis of the nanotubes of the other arrangement, and the arrangements forming at least one array. A resin material having nanoparticles dispersed throughout is disposed among the array(s) of nanofilaments, and cured, and openings may be formed into or through the composite material corresponding to spaces provided in the array of nanofilaments. A composite material according to embodiments forms a microelectronic substrate or some portion thereof, such as a substrate core.

This is a Divisional application of Ser. No. 12/364,435 filed Feb. 2,2009, which is presently pending which is a Divisional application ofSer. No. 11/479,246, filed Jun. 29, 2006 which is now U.S. Pat. No.7,534,648, Issued May 19, 2009.

FIELD OF THE INVENTION

The invention relates generally to the field of semiconductormanufacturing. In particular, the invention relates to compositematerials for substrates and substrate cores.

BACKGROUND OF THE INVENTION

Modern high performance microelectronic devices (e.g. semiconductorchips) operate at substantially higher temperatures than theirpredecessors, which can lead to numerous performance and reliabilityproblems. Some devices operate at temperatures high enough to ignitecertain materials, presenting a thoroughly unacceptable fire danger.Some materials expand or contract in response to thermal variations athigher rates than other materials. When two or more materials withdifferent coefficients of thermal expansion (CTE) are used in amicroelectronic assembly, the extreme variance between operative andinoperative temperatures can cause materials to separate from oneanother, leading to device failure. High temperatures can also causesome materials to soften, particularly organic sheet materials, leadingto structural and/or electrical failures in microelectronic assemblies.

As a result, a microelectronic assembly must be able to efficientlydissipate heat away from a high temperature microelectronic device. Whendesigning and manufacturing electronic assemblies, the materials used toform substrates, packages, and other components closely associated withhigh temperature microelectronic devices must not only be able towithstand high temperatures without being damaged, but must also behighly thermally conductive.

Some methods used to increase the stiffness and lower the CTE ofsubstrates or substrate core materials, include adding or increasing theamount of ceramic or glass filler (fiber) in the substrate materials.While this provides some benefits, it also reduces the manufacturabilityof substrates. In particular, it interferes with formation of holesthrough the substrate, such as plated through holes, by increasing thewear rate of drill bits, increasing the time required to drill holes,and reducing the number of substrates that may be drilled in a singledrilling operation. Further, the reliability of the core material can bedetrimentally affected by the increased amount of glass or ceramicfiller.

Another approach is to use coreless substrates, but these can haveproblems such as increased warpage, low machinability, and blistering.Current materials and approaches simply do not provide a solution whichcombines reliability with highly efficient thermal dissipation in hightemperature conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a method for forming a compositesubstrate core.

FIGS. 2 a-b depict embodiments of aligned nanofilaments disposed at asurface of a substrate.

FIGS. 2 c and 3 depict embodiments of an array of nanofilaments disposedat a surface of a substrate.

FIGS. 4 and 5 depict embodiments of an array of nanofilaments withspaces formed in the array.

FIG. 6 depicts an embodiment of a nanoparticle-filled epoxy resindisposed among nanofilaments of an array.

FIG. 7 depicts an embodiment of openings formed corresponding to spacesformed among nanofilaments of an array.

FIG. 8 depicts a cross-sectional view of an embodiment of amicroelectronic substrate including a composite substrate core material.

FIG. 9 depicts an embodiment of a microelectronic package.

DETAILED DESCRIPTION OF THE INVENTION

As depicted at 110 in FIG. 1, an embodiment of a method 100 includesdisposing nanofilaments in an array at a surface of a substrate.Nanofilaments may include single-walled or multi-walled nanotubes (SWNTand MWNT, respectively) formed of carbon or boron nitride, or carbonnano-fibers. For some embodiments of electrically non-conductivesubstrates or substrate cores, electrically insulating nanotubes such asboron nitride are used. Conversely, for electrically conductivesubstrates or substrate cores, carbon nanotubes or carbon nanofibers canbe used. Carbon nanofibers typically cost less than either carbon orboron nitride nanotubes, but have a lower thermal conductivity thaneither type of nanotube. Therefore, the electrical and/or thermalrequirements of the microelectronic device in which an embodiment of theinvention is implemented will influence the choice of whichnanofilaments to use.

At least one embodiment for disposing nanofilaments thusly employs theLangmuir-Blodgett technique, wherein a monolayer of nanofilaments andsurfactant are uniaxially compressed on an aqueous sub-phase, and theresulting axially aligned (along the long axis) nanofilaments are thentransferred to a planar surface of a substrate, (e.g., a siliconsubstrate). The separation distance between centers of adjacentnanofilaments is controlled by the compression process, producing anarrangement 200 of approximately parallel (aligned) nanofilaments 201 atthe substrate surface 250, as depicted in FIG. 2 a.

A plurality of arrangements may be formed as described above. As in theembodiments depicted in FIGS. 2 b and 2 c, at least a second arrangement202 of approximately aligned nanofilaments 203 is produced and disposedat a surface of a substrate 251, with the long axis of the nanofilaments203 oriented differently from those of the first arrangement. Forexample, the nanofilaments 203 in the arrangement 202 depicted in FIG. 2b are disposed and orientated approximately perpendicularly to thosedepicted in FIG. 2 a. Embodiments of the invention include disposing anarrangement of aligned nanofilaments at a substrate surface 252 so as tosuperimpose at least one other arrangement of nanofilaments alreadydisposed at the substrate surface 252, wherein the nanofilaments 205 ofone arrangement are aligned and oriented approximately perpendicular tothe nanofilaments 206 of the other arrangement to form an array 204 ofnanofilaments in a criss-cross pattern as in FIG. 2 c. Accordingly, atleast one nanofilament 205 in one arrangement will cross over at leastone nanofilament 206 of the other arrangement, as shown at 207. Althoughnanofilaments 205, 206 of an array 204 so formed have some nominalthickness, the thickness of the overall array 204 remains sufficientlysmall, such that nanofilaments 205, 206 of the arrangements within thearray 204 are approximately coplanar with each other, with respect tothe substrate.

While FIG. 2 c depicts a relatively small array, an exemplary embodimentincludes an arrangement of a plurality of such relatively small arrays520, as depicted in FIG. 5. Other exemplary embodiments include arelatively larger array 315 formed at a surface of a substrate 300, asdepicted in FIG. 3, or a combination of relatively larger and relativelysmaller arrays. A relatively larger array 315 may also be formed bycombining a plurality of relatively smaller arrays 204 placed closelytogether at the surface of a substrate 300. In such embodiments, aportion of the periphery of each adjacent array can overlap a portion ofthe periphery of at least one other adjacent array to eliminate gapsbetween the arrays, or be placed closely proximate to each other withoutoverlapping. In this way, nearly any size of array is formed bycombining a plurality of arrays at the surface of a substrate.

An embodiment of a relatively larger array 415, depicted in FIG. 4, alsoincludes spaces 420 formed in the array 415 among the plurality ofnanofilaments. A space 420 provided in an array 415 is an area at asurface of a substrate 400, within the boundaries of which few or nonanofilaments are disposed. The size and position of the spaces 420within the array 415 generally correspond to the size and position ofholes formed in embodiments of a composite material, as will bedescribed. For example, if holes with a diameter of approximately 300micrometers (‘microns’, or ‘μm’) are to be formed, with an approximately400-600 μm pitch between centers of adjacent holes, spaces 420 providedin the array 415 will generally also have their centers positioned atapproximately a 400-600 μm pitch, and a minimum clear area (withoutnanofilaments) of approximately 300 μm as measured in any directionwithin the boundaries of each space 420. Embodiments of the inventionwill typically vary substantially according to the requirements ofdifferent product designs in which they are to be used. Therefore, thedesign requirements will impact the size and position of spaces 420 tobe provided within an array 415. Likewise, spaces 525 can be providedbetween arrays 520 in embodiments including a plurality of relativelysmaller arrays 520, as in FIG. 5, and the design requirements will drivethe layout and spacing of the arrays 520 relative to each other andrelative to locations where holes are to be provided.

In one embodiment, nanofilaments are initially disposed only in thoseareas at the surface of a substrate corresponding to the array, but notdisposed in those areas corresponding to a space. In another embodiment,spaces are formed by selectively removing nanofilaments in an areacorresponding to a space after an array has been formed at a surface ofa substrate. For example, areas of a substrate surface corresponding toa space are treated with a sacrificial material. After disposingnanofilaments at the surface of the substrate, including such treatedareas, the sacrificial material is removed, also removing thenanofilaments disposed in the treated areas. In another example, afteran array is formed at a surface of a substrate, a masking layer isdisposed over the array with openings formed in the masking layercorresponding with areas where spaces are to be formed. Nanofilamentsexposed by the openings are treated with a surfactant, a solvent, orsome other agent capable of removing the nanofilaments from the surfaceof the substrate. Once spaces are formed, the masking layer is removedleaving an array having spaces formed in areas corresponding to holes.

As shown at 120 and 130 in FIG. 1, nanoparticles are dispersedthroughout an uncured epoxy resin, and the resin is disposed among thenanofilaments of an array at the surface of a substrate. Usingnanoparticles as fillers in an epoxy resin provides numerous benefits,including improved thermal stability, due to the low coefficient ofthermal expansion (CTE) of nanoparticles, greater flame retardancy,reduced epoxy resin viscosity, and improved adhesion to externalsurfaces of a composite material formed with the epoxy resin. Dependingon the epoxy resin used and what performance characteristics are desiredin a particular application, the level of nanoparticle loading can beincreased or decreased to alter those characteristics.

According to alternate embodiments, nanoparticles are alumina or silicananoparticles with a diameter of approximately 30 nanometers (‘nm’). Inan exemplary embodiment, a loading of approximately 0.5-1.0 weightpercent (%) of nanoparticles are dispersed in an uncured epoxy resin byconventional sonication or a solution mixing process. In otherembodiments, nanoparticle loadings levels of up to approximately 3.0weight % are used without significant difficulties in nanoparticledispersal or epoxy resin viscosity. As the increase in nanoparticleloading levels increases, uniform dispersal of nanoparticles throughoutan epoxy resin can become more difficult, and/or the viscosity of aresin can increase, potentially hindering complete dispersal of epoxyresin among a nanofilaments array. If relatively higher levels ofnanoparticle loading are beneficial to a substrate or substrate core,for example, up to approximately 10-15 weight % of nanoparticles, anepoxy with a lower initial viscosity can accommodate relatively higherloading while still providing sufficient infiltration into ananofilaments array. In embodiments with relatively low nanoparticleloading, generally untreated particles will be used. However, inembodiments with relatively higher levels of nanoparticle loading, orwhen dispersion of nanoparticles throughout an epoxy resin is poor,silane-treated nanoparticles will also generally provide enhanceddispersion characteristics.

As depicted in an exemplary embodiment in FIG. 6, nanoparticle loadedepoxy resin 630 is disposed at the surface of the substrate 600, and theresin 630 infiltrates among the arrangements of nanofilamentsconstituting the array(s) 620. Epoxy resins, according to embodiments,are any of a class of organic, generally viscous liquid resins,including thermosetting or thermoplastic modified resins typically usedin semiconductor or electronic packaging applications. When so used,epoxy resins can be functionalized to improve thermomechanical and/orelectrical properties, adhesion, and other beneficial properties. Inembodiments, epoxy resins include ether linkages and epoxy groups. Whenused in conjunction with hardeners, curing agents, or catalysts, epoxyresins produce resin systems/networks with excellent electrical and/orthermomechanical properties and good chemical resistance. Although anexemplary embodiment of epoxy resin is referred to throughout thisdescription, the embodiments are not so limited. Non-epoxy based resinsystems including but not limited to novalac-based, cyanate ester-based,biamaleimde-based, and/or polymide-based systems are used according toother embodiments.

As most organic liquids are known to wet the surface of nanotubes, agood interface will generally form between the nanofilaments and epoxyresin 630. As described, an epoxy resin having a relatively lowviscosity will tend to infiltrate more easily among the nanofilaments ofan array 620 than an epoxy resin with a relatively higher viscosity, butembodiments of the invention are not so limited. A number of factors cancontribute to effective infiltration of even a relatively more viscousepoxy resin 630, including the separation distance betweennanofilaments, type and diameter of nanofilaments in the array, thenumber of overlying arrangements of nanofilaments in the array and thealignment angles of nanofilaments in the respective arrangements.

As depicted at 140 in FIG. 1, the disposed nanoparticle-epoxy resinmixture is then cured in situ. Curing is preceded in embodiments bydegassing, to remove dissolved gasses from the epoxy resin. Curing ofthermoset epoxy resins is achieved by exposing the resin to elevatedthermal conditions, according to some embodiments. Curing of epoxyresins in other embodiments is achieved by mixing the resin with anamine or anhydride curing agent, producing a catalytic polymerizationreaction. However curing is carried out in alternate embodiments, acured epoxy resin forms a relatively hard, resistant plastic compositematerial including the array(s) of nanofilaments and dispersednanoparticles.

Following curing of the epoxy, the resulting composite material isseparated from the substrate according to numerous embodiments. In oneembodiment, the composite material is delaminated from the substrate byapplying a mechanical force sufficient to overcome the adhesive forcebonding the composite material with the substrate. For example, amechanical force generated by forcing a wedge into the interface betweenthe composite material and the substrate will exert a separating force,as will a peeling force caused by pulling a substrate and a compositematerial in opposite directions. Delamination can be aided by applying arelease material to the surface of the substrate prior to disposing thenanofilaments and epoxy at the substrate surface, and/or by using asurfactant during separation, thus reducing the adhesive forces betweenthe composite material and the substrate. In another embodiment, asacrificial material is disposed at the surface of the substrate priorto disposing the nanofilaments and forming the composite material. Afterforming the composite material, the sacrificial material is dissolved byexposure to a solvent or by heating and melting the sacrificialmaterial, thus releasing the composite material from the substrate. Instill another embodiment, the substrate itself is a sacrificial materialthat may be dissolved, abrasively ground away, or otherwisedestructively removed from the composite material. In other embodiments,however, the substrate remains coupled with the composite material, andforms a portion of a microelectronic substrate or substrate core.

As a portion of a substrate or substrate core, a composite material maybe in contact with other electrically conductive materials or elements,such as conductive pathways or planes. In such situations, anelectrically conductive composite material could cause electricalshorting between the conductive elements, or between one conductivelayer and another conductive layer or elements comprising portions of amicroelectronic substrate. To prevent shorting in embodiments, anon-conductive masking material is disposed at the surface of at least aportion of the conductive composite material, interposed between theconductive composite material and the conductive elements or layers. Anon-conductive masking material includes a polymer, a spin-on glass(SOG) material, a nitride or oxide material (e.g., silicon nitride), oranother non-conductive material, according to various embodiments. Inother embodiments, the non-conductive material comprises the substrateupon which the composite material was formed, or a layer formed betweenthe substrate and the composite material, and used to separate thecomposite material from the substrate. A non-conductive masking materialmay be disposed across an entire surface of a composite material or onlyselected portions of it, as needed to prevent electrical shorting.

As depicted in FIG. 1 at 150, openings 725 (e.g., holes) are formedthrough the composite material 730 in embodiments. In some embodiments,openings 725 in a composite material 730 align with correspondingopenings in other materials of a microelectronic substrate to provide anopening formed from one exterior surface of a substrate through toanother exterior surface of the microelectronic substrate, (e.g.,through holes). In other embodiments, openings 725 formed in a compositematerial 730 are presented to an exterior surface of a microelectronicsubstrate, but are not formed through to and presented at anotherexterior surface of the microelectronic substrate, (e.g., blind vias).Openings 725, in an exemplary embodiment, are formed as plated throughholes, which may include vias, microvias, or other conductive throughstructures of a microelectronic substrate.

Openings 725 are formed in embodiments by drilling though a compositematerial 730 in an area corresponding to a space 722 provided in thenanofilament array(s) 720. Drilling may be accomplished using a drillbit, a laser, by selective etching (e.g., dry etch), or other methods.In an exemplary embodiment, projecting members, having a diametercorresponding to the diameter of an opening 725 to be formed, areprovided extending approximately perpendicularly from the surface of thesubstrate at which a composite material 730 is to be formed. When theepoxy resin is disposed at the surface of the substrate, it flows aroundand includes at least a portion of the projecting member. When thecomposite material 730 is separated from the substrate, the projectingmembers are also withdrawn from the composite material 730, leavingopenings formed through the composite material 730, similar totechniques sometimes used in injection molding and other moldingprocesses to form openings in a single molding step. In another similarembodiment, the projecting members are not withdrawn from the compositematerial 730, but may be a sacrificial material that is dissolved orotherwise destructively removed, leaving an opening in each portion ofthe composite material 730 previously occupied by a projecting member.In still another embodiment, such as when the substrate remains coupledwith the composite material 730, the projecting members are separatedfrom the substrate and independently withdrawn from the compositematerial 730 to leave openings 725. Another embodiment includes anassembly including projecting members attached to a main body portion ofthe assembly, and arranged to correspond to openings 725 to be formed ina composite material 730. This assembly is placed so that the ends ofeach projecting member opposite from the main body portion are insimultaneous contact with or at least partially penetrate the surface ofthe substrate. The epoxy resin is then disposed and cured, and theassembly is used to simultaneously withdraw all projecting members,leaving openings in the composite material 730. The embodimentsdescribed above are not limiting, and are not to be construed asexcluding openings 725 formed by different approaches in otherembodiments.

As described, embodiments of the invention comprise a composite materialincluding an arrangement of approximately aligned nanofilamentsoverlying at least another arrangement of approximately alignednanofilaments, the longitudinal axis of the nanotubes of the firstarrangement being approximately perpendicular to the longitudinal axisof the nanotubes of the other arrangement, and the arrangements formingat least one array. An epoxy material having a nanoparticles dispersedthroughout is disposed among the array(s) of nanofilaments, and cured,and openings may be formed into or through the composite materialcorresponding to spaces provided in the array of nanofilaments. Acomposite material according to embodiments forms a microelectronicsubstrate or some portion thereof, such as a substrate core.

A microelectronic substrate is a package substrate 800, as in FIG. 8, towhich a semiconductor device is physically and/or electrically coupledto form a semiconductor package in an embodiment of the invention. Inembodiments where a composite material 815 forms a substrate core, theoverall substrate 800 containing the composite substrate core 815 islikewise used as a microelectronic substrate for a semiconductorpackage. A composite material 815 will be an interior layer (e.g.substrate core) of a microelectronic substrate 800 located betweenadjacent materials 805, 820 in embodiments as depicted in FIG. 8, orwill be an outer layer, or a plurality of layers of a microelectronicsubstrate 800. In embodiments, a nonconductive mask layer 810 isdisposed between a surface of a composite substrate core 815 and anotherlayer 805, material, or feature (i.e. conductive feature) of amicroelectronic substrate 800. Openings formed through a compositesubstrate core may transit completely through the microelectronicsubstrate, as at 825, or they may penetrate only partially though themicroelectronic substrate, as at 830.

As in an embodiment depicted in FIG. 9, a composite substrate corematerial forms a portion of a microelectronic device package 900comprising a microelectronic device 903 electrically and/or physicallycoupled with a microelectronic substrate 915. A microelectronic devicepackage 900, according to alternate embodiments, is used in a computersystem such as a normally stationary computer system (e.g., desktop orserver) or a portable computer system (e.g., notebook computer, palmtopcomputer, tablet), a portable audio playing system (e.g., memory chip ordisc drive based audio players), a video game system (e.g., configuredfor connection to a television display), or another electronic system. Amicroelectronic device package, according to alternative embodiments,include a flip chip device, a multichip module, a multiple-core singlechip device, or others as are known and used in electronic systems.

The foregoing detailed description and accompanying drawings are onlyillustrative and not restrictive. They have been provided primarily fora clear and comprehensive understanding of the embodiments of theinvention, and no unnecessary limitations are to be understoodtherefrom. Numerous additions, deletions, and modifications to theembodiments described herein, as well as alternative arrangements, maybe devised by those skilled in the art without departing from the spiritof the embodiments and the scope of the appended claims.

We claim:
 1. A computer system, comprising: a microelectronic substrateincluding a composite material, the composite material comprising: aresin; a plurality of nanoparticles dispersed within the resin; and atleast one array of nanofilaments at least partially included within theresin, the nanofilaments forming a first approximately alignedarrangement and a second approximately aligned arrangement, the secondarrangement being approximately perpendicular to and approximatelycoplanar with the first arrangement, and at least one nanofilament ofthe second arrangement crossing over at least one nanofilament of thefirst arrangement; and a microelectronic device coupled with thesubstrate.
 2. The computer system of claim 1, wherein the nanofilamentsare selected from one of a group consisting of carbon nanofibers, carbonnanotubes, and boron nitride nanotubes.
 3. The computer system of claim1, wherein the nanoparticles are selected from one of a group consistingof untreated silica nanoparticles, silane coated silica nanoparticles,untreated alumina nanoparticles, and silane coated aluminananoparticles.
 4. The computer system of claim 1, wherein the resin isselected from one of a group consisting of epoxy-based, novalac-based,cyanate ester-based, biamaleimde-based, and polymide-based resinsystems.